The method hitherto employed for drying granular solids in an inclined heated screw flight conveyer consists of introducing the wet solids at the lower end and withdrawing a mixture of hot dry solids and vaporized liquid at the opposite end, the heat necessary to vaporization being usually transferred through the conveyor walls, though transfer through an internally heated screw flight is also possible. The heat required to accomplish the drying of the solid material consists of the sensible heat needed to raise both solid and liquid to the discharge temperature, plus the heat of vaporization of the liquid. In addition, if it is desired to recover the separated vapor in liquid form, the heat of condensation would have to be removed requiring additional heat exchange equipment.
It is an object of this invention to reduce the heat required to dry the particulated material and to recover the separated vapor in condensed liquid form. The nature of other objects of the invention will be apparent from a consideration of the descriptive portion to follow.